514 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the present time, and, as far as they go, they point to a modifying in- 

 fluence upon a plastic growth such as that of hair. Broadly speaking, 

 one may say that the hair-streams pass in the lines of the least re- 

 sistance on the body of man. The only interpretation which seems even 

 approximately adequate is therefore a Lamarckian one. 



Hairs of South American Edentates.* — Dr. W. G. Eidewood has 

 examined the hairs of the newly discovered skins of Mylodon, for the 

 purpose of comparing them with the existing sloths, anteaters, aud 

 armadillos. His results tend to disprove Lonnberg's theory that the 

 hairs of Mylodon were furnished with an extra-cortex like that of 

 Bradypus and Choice-pus, represented, in the specimens found, by mere 

 traces owing to the condition of the hair. In the absence of the extra- 

 cortex, and in their general structure, the Mylodon hairs resemble more 

 closely those of Talusia than those of the living sloths. This is not, 

 however, to be regarded as indicating that Mylodon is related to the 

 armadillos rather than to the sloths, but merely shows that, like the 

 anteaters and armadillos, Mylodon has a generalised type of hair struc- 

 ture, a type still represented in the living sloths in the basal part of 

 the hair. 



Body Temperature and Respiratory Exchange in Monotremes and 

 Marsupials, f — Dr. C. J. Martin finds that Echidna is lowest in the 

 scale of warm-blooded animals ; its attempts at homothermism fail to an 

 extent of 10° when the environment varies from 5° to 35° C. During 

 cold weather it hibernates for 4 months, with a temperature only a few 

 tenths of a degree above that of its surroundings. The production of 

 heat is proportional to the difference in temperature between the Echidna 

 and its environment. At high temperatures it does not increase the 

 number and depth of its respirations ; it has no sweat-glands ; it exhibits 

 no evidence of varying loss of heat by vaso-motor adjustments of super- 

 ficial vessels in response to external temperature. 



In Ornithorhynchus there is a distinct advance. The body temperature, 

 though low, is fairly constant ; there are abundant sweat-glands on the 

 snout and frill, but none elsewhere ; the production of carbonic acid 

 with varying temperatures of environment indicates that the duckmole 

 can modify heat-loss as well as heat-production ; its respiratory efforts 

 do not increase with high temperatures. 



Marsupials show evidence of utilising variations in heat-loss to an 

 extent greater than the duckmole, but less than higher mammals ; their 

 respirations slightly increase in number at high temperatures. 



Variation in production of heat is the ancestral method of homo- 

 thermic adjustment. By developing a mechanism by means of which it 

 can vary production in accordance with loss of heat, the warm-blooded 

 animal has overcome one disadvantage of cold-blooded animals, viz. that 

 activity is dependent on external temperature. It has thereby increased 

 its range in the direction of low temperatures. Later, by develojnng a 

 mechanism controlling loss of heat, it has increased its range in the 

 direction of high temperatures, and has also rendered body temperature 



• Quart. Journ. Micr. Sci., xliv. (1901) pp. 39;>-lll (I pi.), 

 f Proc. Roy. Soc, lxviii. (1900) pp. 352-3. 



